Transmission of ultrasound pulses is actually energy traveling of acoustic pulses in transmitting medium. If there is acoustic impedance during the transmission of the ultrasound pulses, the acoustic impedance will resist the movement of the ultrasound pulses. Currently, it is supposed that speed of the ultrasound pulses is fixed in the same medium during the transmission. But, in the invention, the speed of the ultrasound pulses is considered as gradually reduced during the transmission due to the acoustic impedance of the transmitting medium, which gradually depletes the energy of the ultrasound pulses. According direct relationship between the acoustic impedance and a speed of the ultrasound pulses in the transmitting medium, higher speed of the ultrasound pulses will meet higher acoustic impedance and consume more its energy during the transmission. So, the question is if the speed of the ultrasound pulses can still keep the same as currently supposed when its energy is gradually reduced until exhausted? If the speed of the ultrasound pulses is gradually reduced during transmission, the detecting depth may be wrong based on calculating the detecting depth with fixed ultrasound speed for the ultrasound pulses with different frequencies.
Comparing lower frequency of the ultrasound pulses, higher frequency of the ultrasound pulses has larger attenuation coefficient and thus is more readily absorbed in the transmitting medium, which limits the detecting depth of the ultrasound pulses. So, if there is way to increase the detecting depth for high frequency ultrasound?
Ultrasound pulses can be reflected by motionless or moving objects, and it is currently considered that forward moving objects can compress the frequency of the ultrasound pulses and reversely moving objects decompress the frequency of the ultrasound pulses. So, Doppler has been widely used to measure the velocity of the moving objects based on frequency shift, such as medical ultrasound machine and Doppler radar. In Doppler of the pulsed wave ultrasound, aliasing is explained with insufficient Doppler sampling rate of the frequency domain analysis. But, the theory of the frequency domain can not completely solve the aliasing problem in Doppler of the pulsed wave ultrasound and the color ultrasound.
Thus, there is a need to overcome above problems to provide methods for more accurately calculating the detecting depth of ultrasound pulses, increasing the detecting depth of high frequency ultrasound, correctly calculating the speed of moving objects and correcting the aliasing for the pulsed wave and the color ultrasound.